Many automobile components and vehicle body panels are molded of thermoformable compositions such as thermosetting polymer compositions. However, the automotive industry generally requires that all surfaces visible to the consumer have ‘Class A’ surface quality. At a minimum, such surfaces must be smooth, glossy, and weatherable. Components made of thermoformable compositions often require extensive surface preparation and the application of a curable coating to provide a surface of acceptable quality and appearance. The steps required to prepare such a surface may be expensive and time consuming and may affect the mechanical properties of the thermoset materials.
Although the as-molded surface quality of thermoformable components continues to improve, imperfections in their surfaces due to exposed glass fibers, glass fiber read-through, and the like often occur. These surface imperfections may further result in imperfections in coatings applied to such surfaces. Defects in the surface of thermoformable compositions and in cured coatings applied to the surfaces of thermoformable compositions may manifest as paint popping, high long- and short-term wave scan values, orange peel, variations in gloss or the like.
Several techniques have been proposed to provide thermoformable surfaces of acceptable appearance and quality. For example, overmolding of thin, preformed paint films may provide a desired Class A surface. However, such overmolding is usually applicable only for those compositions capable of providing virgin molded surfaces that do not require any secondary surface preparation operations. Although ‘as-molded’ surface quality has improved, as-molded surfaces of component parts continue to need sanding, especially at the edges, followed by sealing and priming prior to painting. In-mold coating can obviate these operations, but only at the cost of greatly increased cycle time and cost. Such processes use expensive paint systems that may be applied to the part surface while the mold is re-opened slightly, and then closed to distribute and cure the coating.
Surface improvements have also been obtained by the addition of low profile additives. Such additives reduce the “read-through” at the surface by causing minute internal voids due to the high stresses and provide a smoother surface. If the void occurs at the surface however, a defect may result in the finish. The voids also act as stress concentrators, which may cause premature failures under additional stress or may appear at the surface during the general sanding and leave a pit that the painting process cannot hide.
Thermoformable multi-layer laminates are known in the vehicular arts as providing acceptable surface preparation when applied to various automobile components without distorting the quality of the underlying surface or substrate. However, prior art laminates have known to show inter-layer or intra-layer separations, including separations from substrates bonded to the laminates. Moreover, the various layers of the multi-layer laminate compositions may adhere unevenly to each other and/or the surface or substrate to which they are applied. This can result in unacceptable surface qualities in the finished automotive part.
Multi-layer laminates have traditionally been formed in a variety of methods, including co-injection molding, overmolding, multi-shot injection molding, sheet molding, co-extrusion, placement of a film of coating layer material on the surface of a substrate layer, and the like. Co-extrusion methods are especially desirable. Multi-layer laminates formed by co-extrusion are advantageous economically and generally exhibit improvements in cohesion and adhesion relative to the various layers making up the multi-layer laminate. However, some multi-layer laminate compositions are difficult to form by co-extrusion. Thus, it has been difficult to provide formable multi-layer laminates that have a desirable balance of properties with respect to adhesion to a substrate and surface quality but are also able to be co-extruded.
Therefore, there continues to be a need for a method for manufacturing thermoformable multi-layer laminate compositions that more effectively adheres to a substrate surface and provides desirable surface quality.